Ovarian biochemical changes associated with chronological aging will be sought as signals for physiological change. Steroid dehydrogenase enzyme activity, in vitro steroidogenesis and also cholesterol metabolism will be measured in rat ovaries. Associated changes in plasma steroid and prolactin levels will be assessed as well as the ovarian response to gonadotrophin. The potential of neonatal hormone imbalance to induce premature physiological ovarian aging will be examined.